Method and apparatus for extrusion of plastics having elastic memory



2 Sheets-Sheet 1 T. J. RHOD ES ET AL METHOD AND APPARATUS FOR EXTRUSIONOF PLASTICS HAVING ELASTIC MEMORY Aug. 25, 1953 Filed June 29. 1950 Aug.25, 1953 T. J. RHODES ET AL 2,649,613

METHOD AND APPARATUS F OR EXTRUSION OF PLASTICS HAVING ELASTIC MEMORY 2Sheets-Sheet 2 Filed June 29. 1950 INVENTOR! 7790/ /40 (A Ave 005$ Byumvzm Aer/.445

AGEN 1' Patented Aug. 25, 1953 Mg e. 13 A'STCS This invention relates.to ametmda d apne ratus for extrusion of plastic 1118413 3131 8 h vinelastic memory, and more partibularlyiti-re elififi to the production oflastic roduotshavinamor exact volume or weight than.-has;heretofor ;beenpossible, by an improved extrusion metho involving the step of measuringa definite len th of the plastic material beingzextrudgdf-twhilethematerial is confined in a definite mos -sectional area.

It has previQlls y teeny-known to producedefinite lengths of extrudedplasti c gnaterials iby p sin the extruded "st-plast e e .a u tingmechanism h i i syn hronized th the rat of cem nt o .thegp asti usoEthel; e ual lengths of Plas c re 59 .1 of re ardl ss lQ variations in tat o extrusion; finch methods forms for molding, l th jatj s definiteume o Washtwit the weight of equal lengths of the extruded p uct may vay by. an averag valueoter than plus or minus 1O jTh1s mean that of theequal lengths material to fill thegolf 1b th a etecti e he f h 'e ailenet 40 trusion. For this reason; theflcrqssj sectional' size of theextruded product is variable, ,ag-di quai lengths of such productsdo'not' havel edualjjvolumes nor equal wei hts. For example, h exrudines nrentione rubber golf ball eenterst' k. t

on ANDIAPPAIRATUS FOR EXTRIJSI N Vl G ELAST C M nhoaesfiojirtomaha JamesJ. Neville, I. *-as q s---- to Uni d fi a es new q a sw e- Applicationdunegll, 1950, Serial No. 171,122

m teriaLsQ that xcessive flash overflows from he molds a d-i s lzhepri cp l ob e t of the pr sent invention is- -to provide-an improvedextrusion method and p a at z whichthe for o ng va iations in thevolumeor weight of the extrudedproducts areminim-i ed w co qu t-savin si mate'- ritavansiim rov men in he q ality" of-the product. AQQQr De toth p s nt invention h xtrusion or tube is provided with a measuringor-metering elementresponsive tothe flow of a definite cnethnf th pl sti-.whileonfin d in a-d finite la qtlone a withinth dieo tuh -Su .'hmetfirins'e m nt' us d' chron z sontrq su a, s mechan m lo at outside ofthe ias I it the ttin m n sm p r s to sever the extruded plastic stream"after a :"definite amount of linear flow' has occurred within the d iien e i't icu t ne mecha mut t 0 trolle intervals es ond ne a de i t iear flow ela fipmea med :whi e t e a i i d a Em pfi -e Qli m rfi 119*??-m, .a i-b th clfqs eei o l a a-"9 thee iilz eiqr th Plast ne ar ly a l.Q i lengths of pre( ;:i s e1y the same volumev or weight. swee I1 w llmo ull underst od fro the f owing detailed deseriptionwhen read with i ei i eni li ni m nyi in in Wmqh: n .7

ig. 1 is a side elevational.view p artly in section, of an apparatusconstructed accordingto the presentlir'i'vehtiom" "Fig. :2 afviey'r ofthe apparatus substantially a1Qes.ihe i 2:2

Bjis a schematic perspective View of a modification of'the'invention;and,

Fig. 's a wiring diagram of the control sysea loyed n'Fijg. '3'. R' 1,'theapparatus shown com.- r a e ii K I it ha r' sla irew H for advancingplastic 'vulcaniz'able 1 rubber' st'ock '12 pparatus under pressure. Thebe rotated by'a suitable driving reek 'may'fbe tree are the e};-

heusiial ho perinot shown) l zijs first advanced through 1 assemblyfjafand thereafter lqile e nbr ete i q 1y 14 of th'e' oharacterdi.Dp1i'c al 'ionofThQI IaSQJ; R des .Seri 'IN 11' B L: 28, 1950. Thepreliminary die assembly 13 is detachably mounted at the delivery head15 of the extruder 10, as by a screw thread It on the outside of the dieassembly. The die assembly has therein a throat, or central restricteddie passage ll, of small diameter. The die passage I1 is defined by anannular member [8 disposed within a recess 19 in the entrance to the dieassembly 13. I n order to enable smooth,"

stream-line flow fof the stock [2 into and out of the die passage H, theannular restricting member 18 is smoothly curved into and out of theorifice IT, as indicated at 20 and 2|.

As is conventional practice, means (not shown) may be provided forheating the extruder Ill and the die assembly I3 to facilitate theextrusion.

The confining tube I4 has an enlarged flange shaped'as to accommodate athin annular lubricant applicator'member 43, which is brazed to and heldin, place by a retaining ring 44 located between the face of the dieassembly [3 and the confining tubelll. A small amount of liquid portion22 at its entrance end, through'which'" bolts 23 pass into the body ofthe die assembly 13 for detachably securing the tube assembly to the dieassembly. The tube l4 has an elongated passageway 25 therein, having thecross-sectional size and shape of the desired preforms.

As shown the preforms are cylindrical raw rub- 2 ber pieces 26. The exitend of the tube 14 is fastened by means of a clamp 21 to a standard 28extending from a suitable supporting frame work 29.

As is disclosed in the copending application referred to previously, itis desirable that the diameter of the passage 25 be greater than thediameter to which the stock I2 would ordinarily swell upon emergingfreely from the restricted passage 11. With the usual vulcanizable softrubber stock, the cross-sectional area of the passage 25 should be fromthree to six times, but preferably from four to five times, that of thedie passage IT.

The forward movement of the plastic rubber has teeth 32 for morepositively engaging the rubber stock. As will be explained in detailbelow, the rate of forward movement of the stock, as measured by thewheel 30, is used to control the speed of operation of a cutting knife33 carried by a rotating fly-wheel 34 located at the exit end of thetube [4.

In order to minimize radial swelling and axial shrinkage of the extrudedproduct, the passage 25 is preferably made sufiiciently long so that thestock is confined therein in the desired shape for at least 3 seconds,and preferably 15 to 20 seconds.

' The stock is caused to fill out the tube l4 in a firmly compactedcondition by a snubber 35 at the exit end of the tube M, which permitsthe extruder screw II to develop substantial pressure within the tube.The snubber 35 has a restricted passageway 36, the entrance to which issmoothly tapered in order that the shaped plastic stock may passsmoothly therethrough without turbulent flow or disruption. For softrubber stocks, the exit passage 36 should have a diameter equal to fromto 95%, preferably about nine-tenths of the diameter of passage 25.

In order that the rate of advancement of the rubber stock adjacent tothe wall of the tube [4, as measured by the wheel 30, shall besubstantially the same as the rate of advancement of the rubber stock inthe center of the passage 25, means is provided for introducing a thincompacted in the desired shape.

lubricant introduced at a constant rate from asuitable positive pumpingsystem (not shown) through the delivery tube 40, passes out under theforward edge of the applicator member 43 onto the surface of the passingrubber column. The member 43 keeps the rubber stock from entering thelubricant distributing passage 4|.

Suitable lubricants for this purpose are liquids which reduce thesurface tackiness of the plastic, and which are not deleterious to theplastic being extruded.

Among such lubricants are soaps, glycerine,

T paraffin oil, and silicone mold release fluid,

which is a mixture of low molecular weight linear polymericorgano-siloxanes.

It is necessary to provide means for the lubricant to escape from thetube M before the plastic stock passes through the restricting passage36 at the end of the tube, so that there will not be an accumulation oflubricant at this point which would result in distortion of the stockwithin the passage 25. For this purpose, a series of small radiallubricant bleed holes 45 is provided in the wall of the tube [4, justbefore the snubbing portion 35.

The measuring wheel 30 is mounted for rotation on a horizontallyextending spindle 45 held in a vertical standard 41, which is secured atits base to the framework 23. A horizontally extending platform 48 ontop of the standard 4? supports an alternator 43 having a driving pulley5!) connected by means of a belt, 5! to another driving pulley 52rotatable with the wheel 33. The alternator 49 is electrically connectedby means of conductors 53 to an amplifier 54 which feeds the amplifiedalternating voltage generated by the alternator 49 to a synchronousmotor By this arrangement, the speed of the synchronous motor 55 isproportioned to the frequency of the alternating voltage, and hence themotor 55' is driven at a speed proportional to the speed of rotation ofthe measuring wheel 39. Power supply wires 56 connect the amplifier to apower source in the conventional manner, while the amplifier isconnected to the motor 55 by conductors 57.

For the purpose of driving the fly-wheel 34 carrying the cutting knife33 at the desired speed, a variable speed transmission 58 is interposedbetween the motor 55 and the fly-wheel 34. The transmission may be setmanually at the desired speed.

In operation, the extruder screw ll forces the plastic stock l2 throughthe restricted die passage I! into the elongated confining passage 25 inwhich the stock is confined under pressure and A thin film of lubricantis continuously applied to the surface of the advancing stock throughthe inlet tube '40 as the stock passes into the passage 25. 'Theadvancing stock 12 causes the measuring wheel to revolve, therebydriving the alternator 49. The speed at which the alternator is driven,and hence the frequency of the electrical signal generated thereby,determines the speed of the synchronous driving motor 55, thereby fixingthe speed of rotation of the fly-wheel 3'4 carrying-the cutting knife3'5 at a rate directly proportional to the linear speed of the rubbercolumn.

The cutting knife 3.3 cuts the plastic stock l2 into lengths 2 5 as itemerges "from the exit end of the tube !'4. The lubricated stock ismomentari'ly reduced in diameter while passing through the restrictedsnubbing passage as, and recovers afteremerging to substantiallythe'size and shape imparted to it within the tube M. The cylindricalpreforms 26 cut off by the rotating knife 33 may be collected in-asuitable-container 59, wherein they may 'be dusted with talc to preventsticking together.

Those skilled in the art will realize that many different controlmechanisms may be employed for controlling the operation of thecuttingmechanism in response to the rate-of flow of the plastic within theconfining die or tube. Fig. 3 shows a preferred modification of theinvention in which plastic stock is extruded froma conventional extruder68 through an elongated die or confining tube 6! having a lubricantinlet 52 for lubricating the plastic in the manner previously described.In this case,'the tube -61 is again provided with a measuring wheel 63inassociation with a-suitable controlling system including a mechanicaldifferential $4 for synchronizing the-speed of a fly cutter 65 forcutting the extruded'plas'tic as it emerges from the-exit of the tube61. The'fiy cutter 65 is driven by a-direct current motor 6% through avariablespeed transmission 6-1 suitably coupled thereto. The motor (SEis also suitably coupled, through a variable speed transmission 68, to ashaft 69 extending from the mechaniealdifieren- 'tial tit. The variablespeed transmissions may be set manually to give a desired ratio betweenthe speed of the cutter 65 and the shaft 59. Another shaft 70 extendsfrom the =oppos'ite endof the mechanical differential '61 and issuitably coupled to the metering wheel 63.

The mechanical differential 6 4 is of the spur gear type and is aconventional gear arrangement so constructed that when the twos'hafts'Ed and "58 extending therefrom are driven at the same speed inopposite directions, the housing l t-of the differential remainsstationary. However, if there is any difference inthe speed at which theshafts 69 and it are driven, then -the housing ll will rotate in thesame direction as the faster of the two shafts at aspeed'equa'l toone-half the difference in the speed of thetwo shafts.

The rotation .ofthehous'ing "ll 'of 'themech'anical difierential 6'4 isutilized to control the "speed of the driving motorfie 'inrespo'nseto'changes in speed of the measuring wheel "63, so' t'hat these two speedsalways'remainin the same ratio. For this purpose, a circumferential ringgear 1'2 fixed to the housing H o'fthe'idifferential"64'is suitablycoupled to a conventional ipotentiometer 13 through a pinion gear'onthe'sh'aft 'df the-potentiometer. rotated at afas'ter or slower speed'thanthe shaft 6'9 by the movement "of the plastic within the tube '61,the mechanical differential housing "H and gear 12 turn 'ina clockwise"or counter -'c'lockwise direction to makea'correspon'dingadjust- Whenthe measuring wheel t3 is ment in the potentiometer T3. Thepotentiometer 13 is electrically connected to a vacuum tube controller15 of conventional construction which is in turn electrically connectedto the compound direct current driving motor 6 3 so as to control theshunt field current thereof, thereby controlling the speed of the motor.When the speed of the motor 66 is thus corrected to its proper relationwith the speed of the measuring wheel 63, then the shafts 69 and 18revolve at the same speed and the mechanical differential housing Hremains stationary. Any increase or decrease -in the speed of the wheel63 caused by a change in the speed of advancement of the plastic, causesa corresponding rotation of the housing H of the mechanicaldifferential, with consequent adjustment of the potentiometer andcorrection of the speed of the motor 68. In this manner, the operationof the fly cutter is synchronized with the speed of advancement of theplastic within the tube 6 I.

Fig. 4 shows the general arrangement of .the electrical connectionsbetween the direct current power supply, the controller 15, the variablepotentiometer l3, and the compound direct current motor 53. The variablepotentiometer 13 includes a resistance element 89, one. end of which isconnected by means of a conductor 8 to the negative terminal of abattery 82 which supplies a bias voltage, while the other end of theresistance element 89 is connected by means of a conductor 85-3 to aconductort l leading .to the positive terminal 85 of the mainpowersupply. The positive power supply line 8 is also connected by meansof a conductor=86to the plate 81 of a triode vacuum tube 88 within thecontroller 15. The variable contact 8'9 of the potentiometer 13,actuated through pinion gear 14 by the movement of the mechanicaldifferential '64 (Fig. 3) is electrically connected by'rneans of aconductor 90 to the grid 9! of the triode 38. The cathode 92 of thetriode is electrically connected by means of a conductor 93 .to one endof the shunt field 94 of the motor 513. The other end of the shunt fieldis electricall connected by a conductor 95 to the positive terminal ofthe bias supply 82 and also to the negative terminal 95 of the directcurrent main power supply by means of a conductor 91. The negativeterminal d6 of the main power supply is also'connected by conductors 91and 95 to the series field 98 of the motor 66. The positive conductor 8dof the main power supply is connected to one brush of the motor 66.

This arrangement is such that the current flowing through the shuntfield 94 of the motor it will vary with the-position of the variablecontact 89 of the potentiometer '13, since the position of the contact,by controlling the relative potential I applied to the grid of thetriode, also determines the amount of current flowing through the triodeand the shunt field 94. The effect of the bias supply 82 is to produce agreater change in the current flowing through the triode for a givenchange in position of the "variable contact 89 of the potentiometer '13.

It will be understood that the cathode 92 of the triode is heated tooperating temperature by the usual filament supply source (not shown)acting on the filament '99.

When the preforms produced in the foregoing apparatus are weighed it isfound that they are remarkably uniform as to weight. For example, in oneactual case of extruding golf ball center prefcrms fromrelatively softvulcan-izable rubber stock, 'it was found-that allpftla'e preforms werewithin plus or minus 3% of the average weight. It is believed that suchuniformity in the weight of extruded preforms has not been obtainablepreviously except by laborious trial and error hand cutting and weighingmethods.

The reason for the uniformity of the preforms obtained by the presentmethod andapparatus is that the measuring element, such as the wheel 38,which controls the cutting knife, is responsive to the linear speed ofthe plastic while confined within a die or tube of definite, constantcrosssectional area. Since the rate of linear flow through an area ofconstant cross-section controls the cut, the volume or weight of the cutpiece is necessarily constant, independently of any swelling orshrinkage which may take place after the plastic emerges fromconfinement. This is in contrast to conventional methods involvingmeasuring the rate of advancement of plastic :after its emergence fromthe die and using this measurement to cut oil constant lengths of the:advancing product. Such constant lengths are frequently found to varyconsiderably in volume or weight because of uncontrollable variation in'the cross-sectional area of elastoplastic material extruded from aconventional die.

We have illustrated as a preferred form of our invention an apparatusincluding a restricted entrance die, a lubricated confining tube ofconsiderable length, and a snubbing exit passage, all preferablyproportioned as disclosed. The pur pose of this combination, as isexplained in the copending application referred to previously, is tominimize radial swelling and axial shrinkage of the extruded product. Inthis way, we can obtain preforms which not only have substantiallyconstant volume and weight, but which also have essentially unvaryingcross-sectional area and length. This is of particular importance in thecase of such articles as extruded tire tread preforms, which should notonly contain the desired weight or volume of rubber, but which shouldhave a certain definite and unvarying profile and length.

However, We may carry out our invention without using the combination ofrestricting die, elongated tube, andsnubber. Instead, we may simply usea relatively short die, the speed measuring element being responsive tothe rate of flow within the die passage, so that the stock is confinedin a definite cross-sectional area while the speed thereof is beingdetermined. The plastic stock, upon emerging from such a relativelyshort die, will tend to swell radially and shrink axially to anappreciable extent. In such cases, the length and cross-sectional areaof the products out off by the cutter controlled in the manner of thisinvention may vary considerably, but the volume or weight of the productwill still be substantially constant.

When employing a relatively short die or tube in place of the elongatedtube I4, we may sometimes dispense with the liquid lubricant applicatormeans, and use instead a self-lubricating die, such as one made oftetrafluoroethylene polymer as disclosed in U. S. Patent 2,403,476 toKenneth L. Berry et al., issued July 9, 1946. In any case, we providemeans for substantially eliminating friction of the plastic against thewalls of the die passage within which the flow of plastic is beingmeasured, in order that the flow shall be essentially nonlaminar and themeasuring element shall thereby indicate the true volumetric flow of theplastic.

It will be understood that various suitable 8 conventional tachometermechanisms may be substituted for the measuring wheels 30 and 64, andthe speed measurements or indications obtained thereby way be used tosynchronize any conventional cutting mechanism by means of any desiredelectrical, pneumatic or mechanical control system. In some cases it mayeven be suflicient for the speed measuring means to give visualindication of the linear speed of the plastic, the operation of thecutter being controlled manually in accordance with such visualindication.

Having thus described our invention, what we claim and desire to protectby Letters Patent is:

1. An apparatus for cutting a column of plastic in lengths ofsubstantially uniform weight comprising means for forcing a column ofplastic through a passageway, means for measuring any length of plasticwhich passes a cross-section of the passageway, and means operated inresponse to said measuring means for cutting the column of plastic intoequal quantities determined by the length of the column measured withinthe said passageway between each operation of said cutting means.

2. In an extruding and cutting mechanism having means for synchronizingthe operation of a cutter with the speed of extrusion of plasticmaterial from an extruder tube having an extrusion orifice, theimprovement of a speed measuring element located within the extrudertube and spaced from the said extrusion orifice for controlling thesynchronizing means.

3. Apparatus for extruding plastic material and cutting same intolengths containing substantially equal quantities of material comprisinga tube, means for forcing plastic material through said tube, meanswithin said tube for measuring the rate of flow of the plastic materialtherein, means for cutting the extruded plastic material into lengthsand means responsive to said measuring element for synchronizing theoperation of said cutter with the rate of flow of the plastic.

4. Apparatus for extruding plastic material and cutting same intolengths containing substantially equal quantities of material comprisingmeans for advancing the plastic material under pressure, a preliminaryrestricting die, an elongated confining chamber having a crosssectionalarea greater than the area to which the plastic would ordinarily swellupon emerging freely from said restricting die, means for introducing athin continuous film of liquid lubricant to the surface of the plasticwithin said chamber, a snubber at the exit of said elongated confiningchamber, a measuring element for determining the speed of advancement ofthe plastic within said confining chamber, means for cutting the plasticinto lengths after it emerges from the confining chamber, and controlmeans for synchronizing said cutting means with the speed of the plasticwithin the confining chamber as determined by said measuring element.

5. An apparatus for extruding plastic material and cutting same intolengths containing substantially equal quantities of material comprisingmeans for advancing the plastic material under pressure, a preliminaryrestricting die, an elongated confining chamber having a crosssectionalarea greater than the area to which the plastic would ordinarily swellupon emerging freely from said restricting die, means for introducing athin continuous film of liquid lubricant to the surface of the plasticin said chamher, a measuring wheel passing through the wall of saidconfining chamber engaging the plastic and rotatable by the forwardmovement thereof at a rate proportional to the flow of plastic, meansassociated with said measuring wheel for producing an electrical signalproportioned to the rate of rotation of said wheel, means for cuttingthe plastic into lengths after it emerges from the confining passage,and control means for regulating the operation of said cutter inaccordance with the said electrical signal to out 01f lengths of plasticcorresponding to a definite volumetric fiow within the confiningchamber.

6. The method of extruding plastic material having elastic memory andcutting same into lengths containing substantially equal quantities ofmaterial comprising extruding the plastic through a tube, measuring thelinear rate of flow of the plastic while the said plastic is confinedwithin said tube, and cutting the plastic emerging from said tube intolengths corresponding to definite increments of said flow.

7. The method of extruding plastic material having elastic memory andcutting same into lengths containing substantially equal quantities ofmaterial comprising extruding the plastic through an elongatedlubricated tube, measuring the linear rate of flow of the plastic whilethe said plastic is confined within said tube, and

1O cutting the plastic after it emerges from said tube into lengthscorresponding to definite increments of said flow.

8. The method of extruding plastic material having elastic memory andcutting same into lengths containing substantially equal quantities ofmaterial comprising extruding the plastic through a preliminaryrestricting die, causing the plastic to swell to a size greater than thesize to which it would ordinarily swell upon emerging from the saidrestricting die, advancing and lubricating the plastic while confiningit in said swollen size, measuring the linear rate of fiow of the soconfined plastic, and cutting the plastic after it emerges fromconfinement into lengths corresponding t definite increments of saidfiow.

THOMAS J. RHODES. JAlVIES J. NEVILLE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,381,249 Stewart June 14, 1921 1,615,966 Straight Feb. 1,1927 1,743,299 Wiemer Jan. 14, 1930 1,944,464 Richardson Jan. 23, 1934

